</font><font color="blue" class="small">( I wouldn't be too concerned about it bending. It is 3/8" thick, plus he's got the strength of the bucket metal too start with. My setup is almost identical, and I've done a lot of lifting with the angle iron with no problem. )</font>
I guess that really would depend on the size, weight, and strentgh of the tractor. The idea is neat, but I'm 100% certain that without at least some triangle gussets welded on either side of the slots, the angle will bend a whole lot easier than you'd think. The strength of the bucket steel would have nothing to do with the top lip of the angle bending outward. I probably have 15 or 20 twenty foot sticks of 2" X 3" X 3/8" angle in the shop. I've worked with the stuff for decades. If the tractor is over 25 hp or so, I'd say it will definitely bend without reinforcement unless it is only used to drag relatively light objects.
The only other issue I'd see is the chain link sliding off the top. If the bucket tilted forward any, the chain link can slide out of the slot. I only mention these things for safety reasons. Most people don't realize that a 4000 pound tractor can easily jerk over 40,000 pounds of pressure. I don't think anyone would expect a 3/8" piece of angle to be able to hold that jerk stress without gusset support.